Residue analysis of methoxuron and its breakdown product (3-chloro-4-methoxyaniline) by thin-layer and high-performance liquid chromatography with fluorescence detection

Abstract

Dns derivatization prior to fluorescence detection of phenylurea herbicides (after hydrolysis) and their aniline metabolites was further developed for residue analytical purposes with high-performance (HPLC) and thin-layer chromatography (TLC). Metoxuron and 3-chloro-4-methoxyaniline (CMA) were used as model compounds. An increased fluorescence intensity in TLC was obtained by dipping the plates into paraffin-hexane (2:1). A simple derivatization procedure, viz., addition of Dns chloride, evaporation and dissolution, plus overnight reaction, in the acetonitrile-water mixture used as the mobile phase, was developed for HPLC. The fluorescence intensity of Dns-anilines decreases with increase in the number of halogen substituents, and increases if a methoxy substituent is present. The detection limit of Dns-CMA is about 1 ng in both TLC and HPLC. Residue analyses of CMA and metoxuron in water, potato and soil samples involved acetone or dichloromethane extraction, silica gel clean-up, hydrolysis on a TLC plate (for metoxuron), Dns derivatization and HPLC or TLC evaluation. Retention data and recoveries are presented. The detection limits for CMA are 0.001 mg/kg in water, 0.02 mg/kg in potato and 0.2 mg/kg in soil.